This invention relates to pattern definition and, more particularly, to high-resolution sputter-etching techniques for forming such patterns.
It is known to use a patterned layer of titanium as a mask for sputter etching an underlying layer of gold (see, for example, U.S. Pat. No. 3,649,503, issued Mar. 14, 1972.) In turn, the gold pattern so formed may, for example, serve directly as a portion of an integrated circuit or as the x-ray absorptive component of a mask structure for use in x-ray lithography. (A particularly advantageous mask structure including a patterned gold layer is disclosed in a commonly-assigned copending application of G. A. Coquin, J. R. Maldonado, and D. Maydan, Ser. No. 442,921, filed Feb. 15, 1974, now U.S. Pat. No. 3,900,737, issued Aug. 19, 1975).
Of course, the intermediate masking layer of titanium itself must initially be patterned. In U.S. Pat. No. 3,649,503 the desired mask configuration in the titanium layer is delineated by forming a primary mask pattern in a photoresist layer deposited on the titanium. In accordance with the teachings of U.S. Pat. No. 3,649,503, those portions of the titanium that are not covered with the photoresist mask are removed by chemically etching the exposed titanium. The unetched or remaining titanium then serves as the aforementioned mask for sputter etching the underlying gold.
In a number of applications of practical importance wherein very high resolution in the gold layer is desired, it has been found that the resolution initially achieved in the resist layer is severely degraded due to undercutting of the resist layer and excessive etching of the titanium during the noted chemical etching step.
In particular, the significant advantages of submicron resolution achieved in an electron resist material by means of an electron beam exposure system often cannot be realized in practice in underlying layers due to the aforespecified undercutting phenomenon. In some cases, undercutting of as much as 5 microns due to chemical etching has been observed. This obviously completely vitiates the submicron resolution capabilities inherent in electron beam lithography. (A description of an electron beam exposure system capable of forming a submicron pattern in an electron resist layer is contained in a commonly-assigned copending application of R. J. Collier and D. R. Herriott, Ser. No. 461,876, filed Apr. 18, 1974, now U.S. Pat. No. 3,900,737, issued Aug. 19, 1975).
Attempts have also been made at patterning a resist-masked titanium layer by conventional sputter-etching techniques. But in many cases of practical importance, it has been found that the resist-mask material is etched away in the sputtering process before the underlying titanium is completely patterned. This is an especially vexing problem where very high resolution is desired because in such cases an extremely thin, and therefore easily etched away, layer of resist material is used.